Method and apparatus to improve ADS-B security

ABSTRACT

Security of ADS-B transmissions is improved in a first embodiment to detect position spoofing. The annunciated position source may then be compared with the derived source and a determination is made regarding the difference between the results. Any position difference greater than an amount significantly greater than the combination of the error sources is then a cause for concern and can be used to generate an alert. In a second embodiment, alerting may be based on identification spoofing. From these sources a correlated ID is available which will have an associated confidence based on the number of sources and the level of agreement on the information. Aircraft dynamics may be correlated with the announced ID for consistency. A priori information on the aircraft and location, such as schedule information, and normal operations, may be used to assist in the confidence of aircraft identity. In a third embodiment, alerting may be based on spoofing of identity and position.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 11/203,823, filed Aug. 15, 2005, incorporatedherein by reference in its entirety;

Application Ser. No. 11/203,823, filed Aug. 15, 2005 is aContinuation-in-Part of U.S. patent application Ser. No. 10/830,444,filed on Apr. 23, 2004, now U.S. Pat. No. 7,123,192, incorporated hereinby reference in its entirety;

Application Ser. No. 10/830,444, filed on Apr. 23, 2004 is a DIVISIONALof U.S. patent application Ser. No. 10/457,439, filed on Jun. 10, 2003,Now U.S. Pat. No. 6,885,340, incorporated herein by reference in itsentirety;

Application Ser. No. 10/457,439, in turn is a Non-Provisional ofProvisional U.S. patent application Ser. No. 60/440,618, filed on Jan.17, 2003, incorporated herein by reference in its entirety;

Application Ser. No. 10/457,439 is also a Continuation-In-Part of U.S.patent application Ser. No. 10/319,725, filed on Dec. 16, 2002, now U.S.Pat. No. 6,812,890, incorporated herein by reference in its entirety;

Application Ser. No. 10/319,725 in turn is Non-Provisional ofProvisional U.S. patent application Ser. No. 60/343,237, filed on Dec.31, 2001, incorporated herein by reference in its entirety;

Application Ser. No. 10/319,725 is also a Continuation of U.S.application Ser. No. 09/971,672, filed on Oct. 9, 2001, now U.S. Pat.No. 6,567,043, incorporated herein by reference in its entirety;

Application 09/971,672 is in turn a DIVISIONAL of U.S. patentapplication Ser. No. 09/516,215, filed Feb. 29, 2000, now U.S. Pat. No.6,633,259, incorporated herein by reference in its entirety;

Application No. 09/516,215 is a Non-Provisional of Provisional U.S.patent application Ser. No. 60/123,170 filed Mar. 5, 1999, incorporatedherein by reference in its entirety;

Application 10/457,439 is also Continuation-In-Part of U.S. patentapplication Ser. No. 09/516,215, filed Feb. 29, 2000, now U.S. Pat. No.6,633,259, incorporated herein by reference in its entirety;

Application No. 09/516,215 is a Non-Provisional of Provisional U.S.patent application Ser. No. 60/123,170, filed Mar. 5, 1999; incorporatedherein by reference in its entirety;

The present application is Continuation-In-Part of U.S. patentapplication Ser. No. 10/743,042, filed Dec. 23, 2003; now U.S. Pat. No.7,132,982, incorporated herein by reference in its entirety;

Application 10/743,042 is a Continuation-In-Part of U.S. patentapplication Ser. No. 10/638,524, filed on Aug. 12, 2003; now U.S. Pat.No. 6,806,826, incorporated herein by reference in its entirety;

The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 11/031,457 filed on Jan. 7, 2005, incorporatedherein by reference in its entirety;

Application 11/031,457 is a Non-Prov. of U.S. patent application Ser.No. 60/534,706, filed Jan. 8, 2004, incorporated herein by reference inits entirety;

The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 10/756,799, filed on Jan. 14, 2004, now U.S. Pat.No. 7,126,534, incorporated herein by reference in its entirety;

Application 10/756,799 is a Continuation-In-Part of U.S. patentapplication Ser. No. 10/751,115, filed on Jan. 5, 2004, now U.S. Pat.No. 6,992,626;

The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 11/111,957, filed on Apr. 22, 2005, incorporatedherein by reference in its entirety;

The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 11/145,170, filed on Jun. 6, 2005, incorporatedherein by reference in its entirety;

The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 11/203,823, filed on Aug. 15, 2005, incorporatedherein by reference in its entirety;

The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 11/209,030 filed on Aug. 25, 2005.

The subject matter of the present application is related to thefollowing issued U.S. Patents, assigned to the same assignee as thepresent invention, all of which are incorporated herein by reference intheir entirety:

U.S. Pat. No. 5,999,116, issued Dec. 7, 1999, entitled “Method andApparatus for Improving the Surveillance Coverage and TargetIdentification in a Radar Based Surveillance System”;

U.S. Pat. No. 6,094,169, issued Jul. 25, 2000, entitled “PassiveMultilateration Auto-Calibration and Position Error Correction”; U.S.Pat. No. 6,211,811, issued Apr. 2, 2001, entitled “Method and Apparatusfor Improving the Surveillance Coverage and Target Identification in aRadar Based Surveillance System”;

U.S. Pat. No. 6,384,783, issued on May 7, 2002, entitled “Method andApparatus for Correlating Flight Identification Data With SecondarySurveillance Radar Data”;

U.S. Pat. No. 6,448,929, issued Sep. 10, 2002, entitled “Method andApparatus for Correlating Flight Identification Data With SecondarySurveillance Radar Data”;

U.S. Pat. No. 6,567,043, issued May 20, 2003, entitled “METHOD ANDAPPARATUS FOR IMPROVING THE UTILITY OF AUTOMATIC DEPENDENTSURVEILLANCE”;

U.S. Pat. No. 6,633,259 issued Oct. 14, 2003 “METHOD AND APPARATUS FORIMPROVING THE UTILITY OF AUTOMATIC DEPENDENT SURVEILLANCE”;

U.S. Pat. No. 6,806,829, issued Oct. 19, 2004, entitled “METHOD ANDAPPARATUS FOR IMPROVING THE UTILITY OF AUTOMATIC DEPENDENTSURVEILLANCE”;

U.S. Pat. No. 6,812,890, issued Nov. 2, 2004, entitled “VOICERECOGNITION LANDING FEE BILLING SYSTEM”; and

U.S. Pat. No. 6,885,340, issued Apr. 26, 2005, entitled “CORRELATION OFFLIGHT TRACK DATA WITH OTHER DATA SOURCES”.

FIELD OF THE INVENTION

The present invention relates to a Method and Apparatus to improve ADS-BSecurity. In particular, the present invention relates to techniques forusing other data sources to validate the annunciated position of anaircraft and validate the annunciated identity of an aircraft asreported by ADS-B.

BACKGROUND OF THE INVENTION

Automatic Dependent Surveillance (ADS), a new standard adopted by manyaviation authorities worldwide offers a great leap forward in aircraftsurveillance capabilities. More information is made available thanbefore with conventional primary and secondary radar technologies, andas ADS-B does not require major conventional radar groundinfrastructure, the cost of implementation is far lower than Prior Arttechniques.

Whether ADS will allow the decommissioning of primary conventionalradars is the subject of many ongoing debates. However, most nations seethe benefits in the implementation of a relatively low cost flighttracking technology. Countries with vast tracts of land or mountainousterrain that is not viable for conventional radar see the technology ashighly cost beneficial.

Countries ranging from Australia to Taiwan have adopted ADS-Btechnology. Many working groups consisting of members of theinternational aviation community have participated in the development ofmany aircraft avionics and ground systems standards, for example RTCASpecial Committee 186, which developed the ADS-B MASPS. A selection ofsome of the Committee's issue papers are listed below, and incorporatedherein by reference. Additional papers, on the subject are availablefrom http://adsb.tc.faa.gov/RFG.htm, also incorporated herein byreference.

The aforementioned Issue Papers, all of which are incorporated here byreference:

File Name (*.PDF) Size Date Status Description ASA-ASAS-Issue- 1.5 mNov. 23, 2004 — ZIP file containing all submitted issue Papers.zippapers (1-20) Blank ASAS Issue  8k — — Blank submission form Paper.zipIP01 TCAS ASA 14k Apr. 23, 2003 Withdrawn TCAS Platform Usage MASPSIssue IP02 Degraded Target 16k Apr. 23, 2003 Closed Degraded TargetUtility Indicator Utility Indicator IP03 ASSAP 19k Apr. 23, 2003 ClosedSpecifications are needed for ASSAP Ownship Data processing of Ownshipdata and Processing interfaces from ASSAP to the ADS-B transmittingsubsystem IP04 Unknown SIL. 15k Apr. 23, 2003 Open Legacy GPS Systemsare unable to provide values for SIL IP05 Application 38k Apr. 23, 2003Deferred Recommendations for changing the Names and Acronyms naming andacronym conventions for Airborne Surveillance Applications. IP06 MinimumData 17k Apr. 23, 2003 Closed Cautions against placing minimum QualityRequirements output requirements on ADS-B data. IP07 Enhanced SIL 21kApr. 23, 2003 Closed Requests that SIL definitions be Bit Definitionsextended to include intermediate values than those specified in DO-242A.IP08 CDTI - Ownship 59k Apr. 23, 2003 Open Proposal to address CDTIdisplay Directionality requirements when ownship loses itsdirectionality information. IP09 CDTI - Display 54k Apr. 23, 2003 OpenProposal for how CDTI symbology of Position might represent positionuncertainty. Uncertainty IP10 CDTI - Altitude 15k Jun. 18, 2003 OpenRequests clarification on best choice of Usage altitude source (i.e.baro vs. geo) for determining relative and absolute altitude ofdisplayed CDTI traffic. IP11ASA - Continuity 64k Jan. 13, 2004 PendingIdentification of an inconsistency of in Tables 2-3 & 3-1 continuityrequirements between Tables 2-3 and 3-1 in ASA MASPS. IP12 ASA - Air-66k Jan. 13, 2004 Pending Problems with ASA MASPS air/Ground Grounddetermination when A/V has no Determination automatic detection means.IP13 ASSAP - TIS-B 58k Feb. 13, 2004 Pending Request to coordinate withWG2 that the Registration TIS-B MASPS requires the appropriateregistration functions between ADS-B and ground sensors such as SSR.IP14 STP - Velocity 64k Sep. 10, 2004 Pending Proposal for new ADS-Bfield to convey Lag Indicator velocity tracker lag. IP15 ASA - ADS-B 66kSep. 10, 2004 Pending Question as to whether there needs to be OUT PowerSwitch a requirement for ADS-B Out systems to have an ON/OFF switchavailable to the pilot IP16 ASA - Surface 58k Sep. 1, 2004 PendingProblem of Surface Vehicles which Vehicles in Tunnels operate on intunnels under runways and taxiways. How do Aircraft track these vehicleswithout placing them on the runways or taxiways? IP17 CDTI - ADS-B 25kNov. 3, 2004 Open Summation of issue of whether or not TCAS Symbol CDTIshould introduce directionality Directionality indication onto TCAStargets. IP18 CDTI - Velocity 718k  Nov. 3, 2004 Open Summation ofissues related to using Vector Issues velocity vectors for CDTI targets.IP19 ASSAP - 17k Nov. 2, 2004 Pending Since there is no means on thereceive Received NUC means side to determine if transmitting DO-260Integrity unknown compliant systems are also TSO C166 compliant,integrity must be assumed to be ZERO for received data. IP20 ASSAP -Limit 18k Nov. 2, 2004 Pending NIC & NAC values of 9 or greater are ofNIC & NAC to 8 defined with vertical considerations. or less Sinceinitial STP MOPS will not address these factors, ASSAP must not usevalues greater than 8 for these fields.

The FAA has also successfully used ADS-B in a program called CAPSTONE,(See, http://www.alaska.faa.gov/capstone/, incorporated herein byreference). The Taiwan CAA started a combined ADS-B and multilaterationprogram in the past few years as detailed on the website:http://www.caa.gov.tw/files/org/CNS_ATMSite/Surveillance.htm, alsoincorporated herein by reference.

The Taiwan CAA website contains a good description of ADS-C. The websiteexplains that in order to meet the ADS operational requirements, thefollowing four types of contract are supported. The first is the Demandcontract 150, in which an aircraft provides data immediately and onlyonce illustrated in FIG. 1, (ADS-C demand contract model). Referring toFIG. 1, control center 140 may send a request 110 for a transmission toaircraft 120. This request 110 may include a transmission number andtransmission time (current time). The request is generally sent onceonly. In response to the request 110, aircraft 120 sends a messagetransmission 130 which may include aircraft identification and locationdata and an end of transmission signal. The control center 140 may thenuse this information to update aircraft position information on acontrol screen or the like, or for other purposes.

The second type of contract is the Periodic contract 250, in which anaircraft provides data periodically as shown in FIG. 2 (ADS-C periodiccontract model). Referring to FIG. 2, control center 240 may send arequest 210, which includes a transmission interval of X minutes, toaircraft 220. Aircraft 220 then sends a reply transmission 232 and thenafter the X minute (or other time interval) a second transmission 234,and a third transmission 236, and so forth. Each transmission 232, 234,236, et al. may include aircraft identification and position informationas well as other aircraft information. The control center 240 may thenuse this information to update aircraft position information on acontrol screen or the like, or for other purposes.

The third type of contract is the Event contract, in which an aircraftprovides information when certain events are detected by aircraftavionics as shown in FIG. 3 (ADS-C event contract model). In the Eventcontract, a transmission may be generated by the aircraft whenever oneor more events occurs. Examples of such events may include a way pointchange 310, in which the aircraft passes through a waypoint and/or headstoward another waypoint on an airchart. Another event example mayinclude a speed change 320 in which the aircraft velocity changes (inthis example from mach 0.82 to Mach 0.78). A third example is analtitude change, in which an aircraft changes from a particular latitudeor from an assigned altitude. A fourth example is a heading/trackchange, in which an aircraft changes from a particular heading orpredetermined track. These four examples of events are not inclusive,and other events may be used to trigger event reporting.

The fourth type of contract is the Emergency contract, in which anaircraft provides data, in the case of an emergency. In this type ofcontract, a transmission is generated if one or more emergencyconditions are triggered, including automatically determined emergencyconditions (loss of cabin pressure, engine out, or the like) and pilotindicated emergencies.

With ADS-B, the aircraft transmits aircraft parameters derived from anon-board navigation system via a broadcast data link to other aircraftor the ground control stations, and can be used to monitor the airportsurface status as illustrated in FIG. 4 (ADS-B application). Referringto FIG. 4, aircraft 420 may derive position information from signalsreceived from (for example) global positioning system satellite 460.When interrogated by air traffic radar 445 or in response to otherindicia, aircraft 420 may emit transponder data (e.g., identificationand/or altitude data and/or other data), which may be received by radar445 such that Air Traffic Management center 440 may track the aircraft.

In addition, aircraft 420 may emit an ADS-B signal, which may bereceived by antenna 470 and/or other aircraft 425. ADS-B data mayinclude information as to aircraft position and altitude, aircraftidentification, and other data. This data may be used to identify andtrack aircraft and also provide other features, such as collisionavoidance.

ADS-B signals may also be multilaterated by measuring the timedifference of arrival (TDOA) at multiple antenna sites 470 to indicateaircraft position. The assignee of the present application has developeda number of techniques for implementing such multilateration, asdescribed in the various Patents and applications previouslyincorporated by reference.

Other aviation authorities have also embraced the use of wide areamultilateration coupled with ADS-B, including Austrocontrol as discussedin Aviation Week and Space Technology, Mar. 7, 2005, page 44-45,incorporated herein by reference. Some detractors of the technology haveraised security concerns, such as Darryl Phillips, who wrote anddistributed ADS-B, Automatic Dependent Surveillance—Broadcast Will ADS-BIncrease Safety and Security for Aviation? first written in Mar. 1999,revised Jul. 2000, by Darryl H. Phillips, AirSport Corporation, 1100West Cherokee, Sallisaw Okla. 74955. See,http://www.airsport-corp.com/adsb2.htm, also incorporated herein byreference.

Other companies have also raised some security concerns and have come upwith various solutions including secure communications links. See, forexample Published U.S. Patent Application Publication No. 20040086121,entitled Secure Automatic Dependent Surveillance, also incorporatedherein by reference. Others have attempted to develop methods to fusedata from disparate sources, attempting to build high confidence or“robust” data fusion processes, as illustrated for example in PublishedU.S. Patent Application Publication No. 20040130479, also incorporatedherein by reference.

Another security concern is the prevention of a pilot (or terrorist)turning off the ADS-B transponder, as was the case with the hijackedaircraft on Sep. 11, 2001. This has lead to many methods such asPublished U.S. Patent Application Publication Nos. 20040148067 and20030060941, entitled Uninterruptible ADS-B System for AircraftTracking, both of which are incorporated herein by reference.

U.S. Pat App 20030193409 describes a method and apparatus for trackingaircraft and securing against unauthorized access. This approach usesthe aircraft's derived surveillance information in conjunction with GISdata to determine if an aircraft is off course. Other methods includebuilding confidence levels in target positions using correlationtechniques, such as that described in Published U.S. Patent ApplicationNo. 20030154018, entitled Multi-source target correlation, incorporatedherein by reference.

As noted in the references cited above, the threat of ADS-B spoofing isof concern to many parties. Altering the existing ADS-B infrastructureto prevent such spoofing would require extensive investment in revisingexisting infrastructure and also changing out ADS-B equipment inexisting aircraft. Such a radical overhaul of the ADS-B system is notcost-effective or practical. A technique for detecting ADS-B spoofingwhich is independent of ADS-B systems is required.

The assignee of the present application has developed an array ofequipment and software and systems for tracking and identifying aircraftbased upon multilateration—using aircraft radio signals to detectposition and identification of an aircraft. As multilateration movedfrom an airport-based system to off airport applications such as widearea it became necessary to find sites off-airport to place the sensors.Off airport sites needed to have power, telecommunication, security andthe ability to position antennas at reasonable heights to overcomeobstructions to achieve line of site to aircraft.

In some of the earlier sites, such as T. F. Green airport in Providence,R. I. and Hyannis Airport in Barnstable, Mass., off airport sitesincluded tops of various buildings, and Government owned communicationtowers. Because of the nature of the equipment at that time includingthe frequency use and large physical size and architecture it was notthought practical that commercial cell phone towers could be used.

SUMMARY OF THE INVENTION

The present invention includes a number of embodiments for improvingsecurity of ADS-B transmissions. In a first embodiment, alerting isbased on position spoofing. Annunciated position may be provided fromvarious implementations of ADS-B such as the Universal AccessTransceiver (UAT), VHF Data Link (VDL), and 1090 MHz ADS-B. Sources suchas wide area multilateration, primary and Secondary Surveillance Radar(SSR), conventional rotating radar, and passive radar, such as theMegadata PASSUR (www.megadata.com), may provide derived position.

The annunciated positions may be correlated through a TrafficInformation Service Broadcast (TIS-B) system. The annunciated positionsource may then be compared with the derived source and a determinationis made regarding the difference between the results. A nominaldifference is expected between the two results as each source hasdifferent error sources, which are generally known and are estimable.

Any position difference greater than an amount significantly greaterthan the combination of the error sources is then a cause for concernand can be used to generate an alert. Averaging of several results maybe used to increase confidence in an alert state. Alerts may then besent to the aircraft, other aircraft, ground positions, and other thirdparties for interception or targeting.

In a second embodiment, alerting may be based on identificationspoofing. Many different sources of the aircraft's ID are shown, rangingfrom surveillance sources (radar, ADS-B, and the like) andcommunications sources (ACARS, CPDLC, and the like). Each of thesesources offers some of form of identity for the aircraft, be it ModeS/ADS-B 24 bit codes, ATC flight number, or flight number. From thesesources a correlated ID is available which will have an associatedconfidence based on the number of sources and the level of agreement onthe information.

Added to this are the dynamics of the aircraft, which include thevelocity, flight level, vertical descent/ascent rates, and the like. Theaircraft dynamics may be correlated with the announced ID forconsistency, for example certain aircraft are capable of operating onlyat certain flight levels or velocities. Aircraft dynamics are computedfrom the various surveillance sources.

Add to this, a priori information on the aircraft and location, such asschedule information, and normal operations, to give a further layer ofdata, which may be used to assist in the confidence of aircraftidentity.

In a third embodiment, alerting may be based on spoofing of identity andposition. In this embodiment, a combination of the elements of first andsecond embodiments are used to give a high confidence alert that aparticular aircraft is announcing an incorrect identity, position, orboth.

All embodiments may be implemented using stand-alone equipment, whichdoes not require an overhaul or modification of existing ADS-Bequipment, either on the ground or on the aircraft. This equipment maybe mounted at an airport, or even off-site. Through equipment redesignto conform with cell tower use, loading, and other factors,multilateration sensor equipment was approved for installation on celltowers, which, due to their high number and availability, made for avery practical way to set up surveillance network of multilateration andADS-B sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the ADS-C demand contract model.

FIG. 2 is a block diagram illustrating the ADS-C periodic contractmodel.

FIG. 3 is a block diagram illustrating the ADS-C event contract model.

FIG. 4 is a block diagram illustrating ADS-B Applications.

FIG. 5 illustrates a first embodiment of the present invention.

FIG. 6 illustrates an embodiment to determine spoofing of aircraftidentity.

DETAILED DESCRIPTION OF THE INVENTION

In a first embodiment, alerting may be triggered based upon positionspoofing. Referring to FIG. 5, the embodiment shows the aircrafttracking data sources 510, 515, 520, 525, 530, and 535 on the left side,where the top three (510, 515, and 520) are derived position and thebottom three (525, 530, 535) are annunciated position. MLAT data source510 may include aircraft position data generated from an aircraft radiosignal multilateration system as described, for example, in theaforementioned Patents and pending Patent Applications previouslyincorporated by reference, from which the present application claimspriority in whole or part.

Annunciated position 555 may be obtained from various implementations ofADS-B such as the Universal Access Transceiver (UAT) 525, VHF Data Link(VDL) 530, and 1090 MHz ADS-B 535, collectively labeled as TIS-B 540.Derived position 545 may be obtained from sources such as wide areamultilateration 510, primary and Secondary Surveillance Radar (SSR) 515,conventional rotating radar, and passive radar 510, such as the MegadataPASSUR (www.megadata.com).

Annunciated position 555 may be correlated through a Traffic InformationService Broadcast (TIS-B) system. The annunciated position source maythen be compared 550 with the derived source and a determination is maderegarding the difference between the results.

A nominal difference 560 may be expected between the two results as eachsource has different error sources and ranges, which are generally knownand are estimable. Any difference significantly greater than thecombination of the error sources is then a cause for concern and can beused to generate an alert 565. Averaging of several results may be usedto increase confidence in an alert state.

Alerts may then be sent to the aircraft, other aircraft, groundpositions, and other third parties for interception or targeting.

FIG. 6 illustrates a second embodiment of the present invention in whichalerting may be triggered by identification spoofing. On the left manydifferent sources of the aircraft's ID are shown, ranging fromsurveillance sources such as radar, ADS-B, and the like, as representedby 610,5215,620,625, 630, and 635 and communications sources such asACARS 605, CPDLC 695 and the like. Each of these sources offers some ofform of identity for the aircraft, be it Mode S/ADS-B 24 bit codes, ATCflight number, or flight number. Aircraft identification may be obtainedfrom various implementations of ADS-B such as the Universal AccessTransceiver (UAT) 625, VHF Data Link (VDL) 630, and 1090 MHz ADS-B 635,primary and Secondary Surveillance Radar (SSR) 615, conventionalrotating radar, and passive radar 610, such as the Megadata PASSUR(www.megadata.com), collectively labeled as TIS-B 640.

From these sources a correlated ID 645 may be derived which will have anassociated confidence based on the number of sources and the level ofagreement on the information.

Added to this is the dynamics of the aircraft 670, which is thevelocity, flight level, vertical descent/ascent rates and the like.Aircraft dynamics 670 may be correlated with the announced ID 645 forconsistency, for example certain aircraft are capable of operating onlyat certain flight levels or velocities or the like. A Cessna 150 is notgoing to operate at 35,000 feet, for example, and if aircraftidentification data indicates such a discrepancy, the aircraft dynamicsmodule 670 of the present invention will detect such an anomaly in thedata. Similarly, if the ADS-B signal from a helicopter indicates that itis in fact a 747, the system may detect such spoofing, if the systemshows the helicopter hovering (as determined by position data), a featimpossible for a 747.

Aircraft dynamics may be computed from the various surveillance sourcesshown on the left of the diagram, and aircraft performance criteria maybe manually programmed or retrieved from a number of known aircraftperformance databases. Various aircraft performance indicia may includeminimum (stall) and maximum (VNE) velocities, climb rates, maximumaltitude (ceiling), as well as other performance characteristics.

Add to this, a priori information 675 on the aircraft and location, suchas schedule information, and normal operations, to give a further layerof data that can be use to assist in the confidence of an aircraft'sidentity. For example, if an aircraft is scheduled to arrive at aparticular airport, based upon airline flight schedule information, andthe system shows this aircraft arriving at a different airport,identification of the aircraft may be in doubt.

Compare function 650 weights these factors together—the ID confidence645, as well as the aircraft dynamics 670 and a priori data 675(collectively derived ID 655). Weighting factors may be used todetermine whether an alert 665 should be generated.

In a third embodiment, alerting may be based on spoofing of bothidentity and position. It is possible to implement an embodiment thatuses a combination of the elements of both the first and secondembodiments of FIGS. 5 and 6 to give a high confidence alert that aparticular aircraft is announcing an incorrect identity, position, orboth. In this third embodiment, weighting factors may be applied to eachdata source and moreover, to each comparison of data sources (or groupsof sources). If a number of discrepancies occur, an alert may begenerated.

For example, from a priori data, it may be indicated that a flightscheduled to land at Washington National Airport is in fact, landing atDulles Airport. Of course, such a discrepancy could occur due to weatherconditions, mechanical problems, closed runways, or any number oflegitimate reasons. The lack of correlation of a priori data may or maynot be grounds for generating an alert.

Similarly, position errors can occur due to perfectly innocent causes.For example, if transponder barometric calibration is not properly set,an aircraft may report an incorrect altitude, which when compared toother data may show a discrepancy. Depending upon weighting factors,this error alone may not be enough to trigger an alarm.

However, if this a priori data indicates a discrepancy, and a positionerror is detected between reported and actual position, an alarm may begenerated. This scenario is by way of example only and is not limiting.Weighting factors and combinations of alarm indicia can be fine-tuneddynamically or in the field depending upon the number of false alarmsgenerated and based upon actual experience in the field.

By using data fusion processes pioneered by the Rannoch Corporation,assignee of the present application, the perceived problem of ADS-Band/or other identity spoofing, as described in the Background of theInvention, can be solved. Moreover, since the present invention does notrequire any changes to existing aircraft equipment or ADS-Binfrastructure, the present invention addresses these security concernswithout disrupting the existing ADS-B system.

As noted above, the equipment of the present invention may be installedat an airport or even off-site. Multilateration antennas may be adaptedfor use on cell phone towers to make installation even simpler. As such,a system can be easily and inexpensively installed to detect ADS-Bspoofing and thus prevent or at least warn of the nightmare scenariosdescribed in the Prior Art with regard to possible terrorist use ofADS-B spoofing to conceal true aircraft identity and position.

While the preferred embodiment and various alternative embodiments ofthe invention have been disclosed and described in detail herein, it maybe apparent to those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopethereof.

1. A system for authenticating aircraft identification signals,comprising: a first input for receiving an annunciated aircraft positionand identification from at least one aircraft generated source,indicating identification of at least one of aircraft type, aircraftidentification, flight identification, and aircraft performance, asecond input for receiving a derived aircraft position from anon-aircraft generated source, indicating position and identification ofthe aircraft, indicating identification of at least one of aircrafttype, aircraft identification, flight identification, and aircraftperformance, a comparator, for comparing the annunciated aircraftposition with the derived aircraft position and generating an alarm ifthe annunciated aircraft position is not within a predetermined range ofthe derived aircraft position, and for comparing the annunciatedaircraft identification with the derived aircraft identification andgenerating an alarm if the annunciated aircraft identification is notwithin a predetermined range of the derived aircraft identification. 2.The system of claim 1, wherein the aircraft generated source includesone or more of ADS-B such as the Universal Access Transceiver (UAT), VHFData Link (VDL), and 1090 MHz ADS-B.
 3. The system of claim 1, whereinthe non-aircraft generated source includes one or more of amultilateration system, primary and Secondary Surveillance Radar (SSR),conventional rotating radar, and passive radar.
 4. The system of claim1, wherein annunciated positions and identifications may be correlatedthrough a Traffic Information Service Broadcast (TIS-B) system.
 5. Thesystem of claim 1, wherein the predetermined range is derived from acombination of the error sources for the annunciated position source andthe derived position sources.
 6. The system of claim 1, wherein aircraftperformance comprises dynamics of the aircraft, which include one ormore of minimum and maximum velocities, flight levels, and verticaldescent/ascent rates.
 7. The system of claim 1, wherein flightidentification includes schedule information.
 8. The system of claim 3,wherein the multilateration system includes a plurality of antennas, atleast some of which are mounted to cellular phone towers.